Method and apparatus for managing faults in a ring network

ABSTRACT

A method of managing faults in a ring network may include configuring a ring network to be in a “horseshoe” topology by disabling a communications link from distributing media between a selected pair of adjacent nodes while allowing other communications or non-related media to continue to be distributed via the adjacent nodes. In the event of a failure, the disabled communications path may be re-enabled, and first or second backup communications paths may be employed, where the first backup communications path may use primary connections between adjacent nodes used for primary communications paths normally used to carry the media, and the second backup communications paths may use secondary connections between non-adjacent nodes. The disabled communications path may be dynamically moved in a logical or physical manner in an event of a communications link or node failure to maintain a “horseshoe” topology in the ring network.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/783,620, filed on Mar. 17, 2006. The entire teachings of the aboveapplication are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Two useful attributes for media service delivery, such as video servicedelivery, are network quality and high-availability. On today's HybridFiber Coaxial (HFC) networks, this is achieved because the technologydeployed is mature and the network is largely dedicated to just a singlefunction—media service delivery. However, when moving the media servicesinto a Packet Switched Network (PSN) arena, achieving high levels ofservice quality and availability becomes a challenging task.

Today's HFC video networks are, in general, very scaleable. Severalmillion customers are serviced from large-scale head-end installations,which then feed distribution networks for user access. To compete withHFC networks, an Internet Protocol (IP) video network must be capable ofscaling to a similar capacity. In a typical network architecture,devices must be able to scale from a few hundred users in the earlystages of implementation to multiple-millions of users at the peak ofthe service deployment. Additionally, in typical situations, it becomesnecessary to add other services, such as voice and high-speed data, whena decision is made to provide a “triple-play” offering. All this must beaccomplished without compromising the reliability, quality,manageability, or serviceability of the network.

SUMMARY OF THE INVENTION

A method of managing faults in a ring network according to an exampleembodiment of the invention may include disabling distribution of mediavia a communications link between a selected pair of adjacent nodesamong multiple nodes coupled by communications links to form a ringnetwork. The example method may include configuring primarycommunications paths to traverse the communications links other thanbetween the selected pair of adjacent nodes and configuring primaryconnections to distribute the media to each of the nodes on the primarycommunications path, including the selected pair of adjacent nodes. Theexample method may further include configuring first backupcommunications paths that use the primary connections between adjacentnodes, other than between the selected pair of adjacent nodes, andconfiguring second backup communications paths and secondary connectionsbetween non-adjacent nodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing will be apparent from the following more particulardescription of example embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe example embodiments of the invention.

FIGS. 1A-1C are network diagrams illustrating an embodiment of thepresent invention;

FIGS. 2A-2F are network diagrams illustrating a technique of configuringa network with an embodiment of the present invention;

FIGS. 3A-3D are network diagrams illustrating another embodiment of thepresent invention; and

FIGS. 4A-4C are flow diagrams illustrating embodiments of the presentinvention.

FIGS. 5A-5B are network diagrams illustrating an example embodiment ofthe present invention;

FIG. 6 is a flow diagram of an example embodiment of the presentinvention;

FIG. 7 is a block diagram illustrating example components that may beused in an example embodiment of the present invention; and

FIG. 8 is a table illustrating a hierarchy of backup communicationspaths optionally used in an example embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A description of example embodiments of the invention follows.

An embodiment of the present inventions includes a method orcorresponding apparatus for distributing media in a ring topologynetwork, optionally using Virtual Private Local Area Network (LAN)Service (VPLS). In this embodiment, the network may be designed suchthat there is a logical break in the ring, optionally in the center ofthe ring. The logical break (a) may be between (i) head-end ingress nodeon the ring network receiving media from a head-end node external fromthe ring network and (ii) an adjacent node in the ring network or (b)may be between two adjacent nodes downstream of the head-end ingressnode. In the former embodiment, the head-end ingress node sends themedia in one downstream direction. In the latter embodiment, the ingresshead-end node sends data downstream in two directions on the ringnetwork in a normal scenario. In a failure scenario, data may passcertain segments of the ring twice.

An embodiment of the present invention may leverage VPLS andMulti-Protocol LAN Service (MPLS) technologies. In utilizing VPLS, theembodiment may create a “replicate and forward” methodology formulticast traffic replication. This may be accomplished because the VPLSdomain may appear as a large layer 2 switch when viewed from aprospective of any of the VPLS domain pseudowire (PSW) circuits. MPLSmay be used as the underlying transport for the VPLS PSWs and mayprovide part of carrier-class redundancy.

FIG. 1A is a network diagram of a network 100 illustrating aspects of anembodiment of the present invention. A part of the network 100 isconfigured as a ring network 105 with six nodes 110, which may beaggregation nodes, connected via physical communications links 115. MPLSLabel Switched Paths (LSPs) 120 may be configured in a manner traversingthe communications links 115 and carrying pseudowires 125.Communications traffic, media traffic, or other forms of traffic, suchas narrowband communications or data, ride on the MPLS LSPs 120 orpseudowires 125, as known in the art.

In the network 100 of FIG. 1A, a service provider may configure themultiple nodes 110 and communications links 115 to distribute media inthe ring network 105. According to an embodiment of the presentinvention, the service provider may also disable distribution of themedia on a communications link, such as a communications link 135between a selected pair of adjacent nodes 130 a and 130 b in the ringnetwork 105 in a manner maintaining communications between the selectedpair of adjacent nodes 130 a, 130 b other than for distribution of themedia.

The network 100 may also include a head-end (HE) node 155 that providesmedia (e.g., video content) 165 to the ring network 105 at node S1(i.e., head-end ingress node) of the multiple nodes 110. The media 165may be switched throughout the ring network nodes S2 through S6 at layer2 via VPLS. At each node 110, a “replicate and forward” function may beemployed for true multicast transmission by forwarding the traffic intwo directions: (1) downstream for distribution to a Digital SubscriberLine Access Multiplexer (DSLAM) system 140, FTTx termination devices145, Layer 2 switches, IP routers, Reconfigurable Optical Add/DropMultiplexers (ROADMs), Cable Modem Head-ends, etc., and (2) downstreamto the next node on the ring network 105.

The head-end node 155 may receive media from upstream sources, such as asatellite farm 160 a or a middleware server farm 160 b. Video or othermedia content can be distributed using any of multiple forms ofdistribution technologies, such as spanning tree, Resilient Packet Ring(RPR), token passing, Bi-directional Line Switched Ring (BLSR),Uni-directional Path Switch Ring (UPSR), layer 3 technologies, such as amulticast routing protocol (e.g., protocol independent multi-cast,sparse node (PIM-SM), which may or may or not be MPLS enabled), layer 2technologies, such as VPLS, transparent bridging (without VPLS),Internet Group Management Protocol (IGMP) snooping, point-to-multi pointprotocol, or a layer 1.5 drop and continue mode protocol.

Continuing to refer to FIG. 1A, the ring network 105 has acommunications link 115 that is configured as a logical break 135 withrespect to distribution of the media 165. Thus, the ring network 105 canbe considered a “horseshoe” topology, though the topology describedbelow in reference to FIGS. 3A-3D more clearly illustrates the“horseshoe” topology. The logical break 135, across which distributionof the media is disabled, prevents a loop in the ring network 105. Ifthere is a fault, a typical work-around is employed that is notdependent on the horseshoe topology. In some embodiments, thework-around includes enabling distribution of the media 165 via thecommunications link 175 previously configured with the logical break135.

In the embodiment of FIG. 1A, the two nodes 130 a and 130 b on each sideof the disabled link 135 are aware of the disabled link 135; other nodesmay or may not be aware of the disabled link 135. Thus, the horseshoetopology may be preconfigured in a manual manner or via a NetworkManagement System (NMS).

Benefits of the horseshoe topology for service providers include nothaving to add information to communications nor having to run a controlprotocol to break the loop (e.g., spanning tree (layer 2) or PIM (layer3)). In one embodiment, MPLS may be employed in the ring network 105.VPLS and MPLS may be used for a layer 2 loading, forwarding, orreplication of packets. VPLS allows media service (e.g., video streams)at guaranteed Quality of Service (QoS) dedicated bandwidth (BW) and maybe used to interact with IGMP snooping.

Because VPLS is commonly used to deliver a Virtual Local Area Network(VLAN) type of service, it usually employs a full mesh of MPLS LSPs andVPLS PSWs between the sites of a particular VPLS domain. Thisconfiguration is derived from a need for all sites to know how to reachall of the other sites within their VPLS domain. However, the nature ofIP multicast traffic is somewhat different. IP multicast does notrequire that each of the VPLS domain members knows how to reach allother members in the domain—it only knows how to reach its neighboringnode. This change relaxes the need for full mesh topology, which leadsto a decrease in the required number of LSPs/PSWs employed in thenetwork, thereby simplifying network topology, implementation, andsupport. Then, the multicast traffic may be “replicated and forwarded”on a per node basis, and this may be responsible for ensuring that allrelevant multicast traffic reaches all of the specified downstreamnodes.

FIG. 1B illustrates how the network 100 can be self-healing andresilient. The same IP media content distribution network as FIG. 1A ispresented in FIG. 1B; however, this network 100 has a link cut 170between nodes S1 and S2. In an event a link cut 170 occurs, illustratedas a severed communications link between nodes S1 and S2, a PSW 171,which rides on a backup LSP 172, is employed to get the media trafficfrom node S1 to node S2.

When nodes S1 and S2 detect the link failure 170, they switch over tothe pre-provisioned or signaled backup LSP 172, and an associated PSW171 follows this LSP 172. Traffic then flows from node S1 in acounter-clockwise direction to node S2 via the other nodes (S5, S4, andS3) along the way, and service is restored within a short amount oftime, such as 7 msec. MPLS Fast Re-Route (FRR) technology may beemployed to ensure restoration of distribution of the media within aspecified length of time.

FIG. 1C illustrates a scenario in which there is a complete node failure175. To address this worst case scenario, a second primary LSP 177 maybe provisioned on each node in the ring network 105. This second primaryLSP 177 is not a backup LSP, but actually a second primary LSP thatprovides a redundant connection in an event of a complete node failure175. A secondary PSW 176 rides on the second primary LSP 177 betweennodes S2 and S4. Because of a requirement for backup LSPs to have thesame end nodes as their primary counterparts, this new LSP 177 is aprimary, not a secondary, LSP. However, the new primary LSP 177 may havea lower weight when compared to the preferred primary LSP so that it isused in an event of a preferred primary and backup LSP completefailure—a condition that exists if a node fails, such as node S3.

It should be understood that, following the node failure 175 of node S3,the communications link 115 with the logical break 135 between theselected pair of adjacent nodes 130 a, 130 b is enabled to carry themedia via the PSW 176 that rides across the lower weighted primary LSP177 between nodes S2 and S4. Enabling the initially disabledcommunications link (i.e., communications link 115 with the logicalbreak 135) may occur both in an event of a node failure 175 or, asillustrated in FIG. 1B, a link failure 170.

FIGS. 2A-2F illustrate another embodiment of the present invention inwhich a configuration embodiment of a ring network is illustrated.Referring first to FIG. 2A, a network 200 with a ring network 205employs network nodes 210, including nodes A, B, C, and D. Between thenetwork nodes are physical links 215. On three of the four physicallinks 215 are LSPs 220 a-b, 220 b-c, and 220 c-d. On the fourth of thefour physical links 215, between nodes A and D, is a physical link 215with a logical break 235 with respect to carrying media between nodes Aand D, which are a selected pair of adjacent nodes 230 a, 230 b. Media265 (e.g., video content) may be received from a middleware server farm260 a or a video head-end node 260 b, or other media source (not shown).As illustrated, the media 265 may be dropped from node C to a DSLAM 240,and further distributed to end user terminal devices 245 (not shown).

In the embodiment of FIG. 2A, it is assumed that node A is in a CentralOffice (CO) and has no subscribers receiving the media 265 from it.Nodes B, C and D may have IP DSLAM(s) connected to them. It should beunderstood that the physical ring of the ring network 205 is closed, butthe LSP ring is not closed, i.e., there is no LSP from node D to node Ain this example network configuration and no media traffic flows overthis link, except in cases of failure(s) in the network.

FIG. 2B illustrates a first configuration step in which an LSP 220 a-bis configured from nodes A to B, optionally with a Fast ReRoute (FRR)facility. Primary LSPs are configured on a per hop basis. In this case,an LSP is created to carry communications between node A and node B. Thesame steps are created for nodes B to C and nodes C to D. In oneembodiment, on configuring each primary LSP, a MPLS fast reroute (FRR)facility is employed. This automatically creates a backup LSP 272 a-b inthe opposite direction of the LSP 220 a-b it is backing-up. In theexample of FIG. 2B, this backup LSP 272 a-b is automatically provisionedfrom node A to node D to node C on its way to node B. Note that thebackup LSP 272 a-b is not terminated in a hop-per-hop manner atintermediate nodes A, D, and C, but is transparently passed throughthem. The backup LSP 272 a-b is terminated at node B, which is itsprotect node, as understood in the art. It is also understood in the artthat there is no traffic flow over the backup LSP 272 a-b when it isacting in a standby mode.

FIG. 2C is a diagram illustrating a backup facility LSP 217 betweennodes A and B. MPLS may be employed to facilitate FRR backup LSPs 272b-c and 272 c-d, which are backing-up a primary LSP 220 a-b on a linksegment between two nodes (e.g., node A and node B). The backup LSPs 272b-c and 272 c-d may share the same facility backup LSP 217 or usedifferent facility back-up LSPs. Sharing one facility backup LSP 217 mayconsume less control bandwidth since one large facility LSP can becreated.

FIG. 2D is a network diagram at a next point in configuring anembodiment of the present invention. A backup LSP 220 b-c is createdfrom node B to node C, optionally with a Fast Re-Route (FRR) facility.In one embodiment, a backup LSP 272 a-b is configured when the primaryLSP 220 a-b is configured between nodes A and B.

FIG. 2E is a network diagram illustrating LSPs 220 a-b , 220 b-c, 220c-d configured on the four node network across physical links (notshown) other than the communications link with the logical break 235disabled from distributing media absent a node or link failure in thering network 205. The backup LSPs 272 a-b, 272 b-c, and 272 c-d areoptionally configured on the ring network 205. Having the backup LSPsconfigured allows for rapid recovery from a failure on a differentcommunications link failure or a network node failure.

FIG. 2F illustrates a scenario in which there is a communications linkfailure 270. The backup LSP 272 b-c for node C flows from node B to A,then from node D to node C, recovering media distribution in less than50 msec (in some embodiments) following the communications link failure270. Nodes B and C have drop and loopback configurations 273 a, 273 b,respectively, to distribute the media 265 to its destination(s). Forexample, node C may replicate video traffic onto a primary LSP 220 c-dfrom node C to node D for transporting the video traffic from node C tonode D.

In reference to FIGS. 1A-1C and 2A-2F, it is described above how anetwork can provide an extremely resilient architectural solution fordelivery of IP media services, such as video. However, the previoustopologies suffer from one weakness—a single point of failure at thehead-end ingress node S1. This weakness can be addressed by using adifferent embodiment of the “horseshoe” topology.

As described above in reference to FIGS. 1A-1C and 2A-2F, a logicalbreak (i.e., logical breaks 135 and 235, respectively) in traffic flowmay be installed between the last ring node and the ingress (i.e.,head-end) ring node because, if this break does not exist, multicasttraffic flows backupon itself throughout the ring network. In thetopology examples of FIGS. 1A-1C and 2A-2F, this logical break 135, 235,respectively, is installed between the ingress node S1 and the last nodein the ring S6; however, if the logical break is moved to be more towardthe center of the ring, it becomes possible to avoid having a singlepoint of failure at the head-end ingress node.

FIG. 3A is a network diagram of a network 300 that illustrates anotherembodiment of the “horseshoe” topology. In the example network 300,there are two logical breaks 335 a, 335 b in the ring network 305instead of just one—one logical break 335 a between a selected pair ofadjacent nodes 330 a and another logical break 335 b between thehead-end ingress nodes 330 c and 330 d, Again, these logical breaks 335a, 335 b are used to constrain traffic to a particular side of the ringnetwork 305 during normal operations.

The network 300 includes similar network nodes and communications linksas presented in reference to FIG. 1A. For example, a satellite farm 360a and middleware server farm 360 b provide media 365 to the head-endnode 355. In the normal operational state, traffic flows from thehead-end node 355 into both of the head-end ingress nodes S1 a and S1 b330 c, 330 d, respectively. Each ingress node then forwards traffic onto its particular half of the ring; that is, node S1 a nodes S2 and S3and node S1 b feeds nodes S4 and S5. The physical links 315 with logicalbreaks 335 a, 335 b between nodes S3/S5 and Sa/S1 b, respectively, maybe used for distributing the media 365 only during network faults in oneembodiment. Similar physical links 315, MPLS LSPs 320, and pseudowires325 are employed in the network 300 of FIG. 3A as were employed in thenetwork of FIG. 1A, and the MPLS LSPs 320 and pseudowires 325 are usedin a corresponding manner.

FIG. 3B is a network diagram in which the network 300 has a link cut (orfailure) 370. Recovery after a link failure with this “horseshoe”topology is similar to what was presented in reference to FIG. 1B.Specifically, in one embodiment, upon detection of the link cut 370, thenodes S1 a and S2 neighboring the link cut 370 begin forwarding trafficacross a backup LSP 372 and accompanying pseudowire (PSW) 371. Within 7msec, for example, node S1 a begins forwarding traffic across the backupLSP 372 to node S2. When in the recovery configuration, the trafficflows in an opposite direction as normal traffic flow absent the linkcut 375 a. Node S2 then continues traffic flow to node S3.

FIG. 3C is a network diagram of the network 300 in which a node failure375 a occurs. Recovery after a complete node failure with thisembodiment of the “horseshoe” topology is similar to what was presentedearlier in reference to FIG. 1C. Upon detection of link failuresresulting from the failed node, the neighboring nodes begin forwardingtraffic across a new preferred connection of a secondary PSW. The newPSW is riding on top of a new primary LSP, as understood in the art. Forexample, in the network diagram of FIG. 3C, node S2 has completelyfailed 375 a. This has resulted in failure of all LSPs and PSWsinvolving node S2. When nodes S1 a and S3 detect the failure, apre-provisioned secondary PSW 371 between nodes S1 a and S3 becomes thepreferred traffic path, and service is restored. After the node failure375 a is corrected, the network configuration may be returned to the“horseshoe” topology with disabled communications links 315 havingrespective logical breaks 335 a, 335 b.

FIG. 3D is a network diagram of the network 300 in which one of thehead-end ingress nodes, node S1 a, receiving communications from ahead-end node 355 experiences a complete failure 375 b. Recovery after acomplete head-end node failure 375 b is very similar, in someembodiments, as to what occurs in the node failure of FIG. 3C. Thedifference is that, during recovery, the remaining operational ingressnode, node S1 b, serves the entire ring topology ,not just half as innormal operation.

In the network diagram of FIG. 3D, node S1 a has completely failed 375b. This has resulted in the failure of all LSPs and PSWs involving nodeS1 a. In addition, all customers served by the top half of the ring(i.e., nodes S2 and S3) are in jeopardy of experiencing a loss ofcommunications containing media 365 or other content. When nodes S1 band S3 detect the failure of node S1 a, a pre-provisioned secondary PSW371 between nodes S1 b and S2 becomes a preferred traffic path for theremaining active nodes on the top half of the ring (i.e., nodes S2 andS3) to receive communications with the media 365 or other content. Inthe recovery state, traffic flows from the head-end node 355 into nodeS1 b, across the secondary PSW 371 to node S2 via a communications link315 (previously configured with a logical break 335 a) between networknodes S5 and S3, and then downstream on the top half of the ring (i.e.,from node S3 to node S2). Traffic on the PSW 371 is only forwarded bythe intermediate nodes (S4, S5, S3) and not sent to locally attachedDSLAMs on these intermediate nodes. Once node S2 receives the mediatraffic over the secondary PSW 371, it then continues sending thetraffic downstream to node S3. Note that traffic flowing on the bottomhalf of the ring (i.e., nodes S1 b, S4, and S5) remains unchanged duringthe recovery process in this embodiment.

FIG. 4A is a flow diagram of a process 400 illustrating an embodiment ofthe present invention. The process 400 begins (405) and configuresmultiple nodes and links to distribute media (e.g., video) in a ringnetwork. Configuring the multiple nodes may be done by a serviceprovider in a manual manner or using a Network Management System (NMS).Other typical ways of configuring multiple nodes and links to distributemedia in a ring network may also be employed. MPLS VPLS techniques maybe used to configure the nodes and links. After configuring the multiplenodes and links, the process 400 may disable distribution of the mediaon a communications link between a selected pair of adjacent nodes inthe ring network in a manner maintaining communications between theselected pair of adjacent nodes other than for distribution of the media(415). By disabling distribution of the media on a communications link,the ring network is changed to be a “horseshoe” topology with respect todistribution of the media. The process 400 ends (420) thereafter and isset to adapt to a communications link failure or node failure in amanner as described above in reference to FIGS. 1A-1C, 2A-2F, and 3A-3D.

FIG. 4B is a flow diagram of a process 401 that includes the configuring(410) and disabling (415), as described above in reference to FIG. 4A,and also includes distributing the media (425) during an operationalstate of the network. Thus, FIG. 4A may relate to an example in which amanufacturer or distributor configures the network to operate accordingto an embodiment of the present invention, and the example embodiment ofFIG. 4B may relate to a service provider (or other party) in which theservice provider configures a network and distributes the media on thenetwork, optionally with contribution from a media content provider,such as a video distributor.

FIG. 4C is a flow diagram of a process 402 that may be used in thenetwork embodiments of FIGS. 1A-1C or FIGS. 3A-3D. The process 402begins (430) and adds media to a head-end ingress node on a ringtopology (435) receiving media from a head-end node, as described inreference to FIGS. 1A-1C and 3A-3D. A determination may be made as towhether the head-end ingress node is a single node or a pair of nodes(440). The process 402 continues in two different, but similar, pathsdepending on whether the head-end ingress node is a single node or apair of nodes, as described above in reference to FIGS. 1A-1C or FIGS.3A-3D.

If the ingress node is a single node, the process 402 determines whetherthe ingress node is one of the nodes in the pair of selected adjacentnodes between which the communications link is disabled (445). If theingress node is one of the nodes in the selected pair of adjacent nodes,the media is distributed in one direction on the ring topology (450). Ifthe ingress node is not one of the nodes in the selected pair ofadjacent nodes (445), the media is distributed in two directions on thering topology (455). Either way, the process 405 continually orcontinuously determines whether there is a link or node failure (460).If there is no failure (460), the process 402 continues to distributethe media downstream in one or two directions (450, 455) on the ringtopology. If there is a link or node failure, the communications linkbetween the selected pair of adjacent nodes is enabled to distribute themedia (465). After the communications link is enabled, the media isdistributed via the communications link between the selected pair ofadjacent nodes until the failure is corrected (470). In someembodiments, a PSW riding on an LSP, which traverses the enabledcommunications link and other communications links, is employed todistribute the media.

In an event the failure is corrected, it should be understood that thecommunications link between the selected pair of adjacent nodes mayagain be disabled to re-establish the “horseshoe” configuration asdescribed above in reference to FIGS. 1A and 3A.

If the head-end ingress node connected to a head-end node is a pair ofnodes (440), distribution of the media on a communications link betweenthe pair of ingress nodes is disabled (475). Media is thereafterdistributed (480), and continual or continuous checking as to whetherthere is a link or node failure (485) ensues. If there is no failure,distribution of the media (480) continues. If there is a link or nodefailure, then, if the failure node is a node in the pair of head-endingress nodes, the distribution of the media on the communications linkbetween the selected pair of adjacent nodes is enabled until the failedingress node is fixed (i.e., in a working state) (495). If there is alink failure or a node failure that is not one of the pair of ingressnodes (485), distribution of the media on the communications linkbetween the ingress nodes and the selected pair of adjacent nodes isenabled until the link or node is fixed (490). Thereafter, distributionof the media (480) continues in the failure recovery configuration untilthe failed node or communications link is fixed. Once the node orcommunications link is fixed, the network configuration can return tothe initial state of a “horseshoe” configuration.

FIG. 5A is a network diagram illustrating an aspect of an exampleembodiment of the invention. The network diagram includes a network 500,which includes a ring network 505 with multiple nodes 510 interconnectedvia communications links 515. In the ring network 505, there are primaryLSPs 520 traversing the communications links 515 and primary VPLSconnections 525 riding on the primary LSPs 520. A logical break 535 a isinitially configured between a selected pair of adjacent nodes 530 a,530 b, thus creating the “horseshoe” topology in the ring network.

In an event of a link failure (e.g., link cut) 570, an exemplaryembodiment of the invention engages a primary backup LSP 572 and primarybackup VPLS connection 571 to carry media or network communicationsbetween nodes F and E. To do so, the initially configured logical break535 a is enabled, and a logical break 535 b is “logically moved” to thecommunications link 515 where the physical link failure 570 occurs. Itshould be understood that computer memory, such as a data table ormemory register, may change states or not change states, depending onthe implementation, to reorganize the “horseshoe” topology from (i)having a disabled communications link 515 between the selected pair ofadjacent nodes 530 a, 530 b to (ii) having a disabled communicationslink 515 where the link failure 570 occurs, such as between adjacentnodes E and F. After the link failure 570 is repaired, the logical break535 a can be configured again between the selected pair of adjacentnodes 530 a, 530 b.

FIG. 5B is a network diagram of the network 500 illustrating anotheraspect of the example embodiment of the invention. In an event of a nodefailure 575, the example embodiment of the invention may enable theinitially configured logical break 535 a and logically assert a logicalbreak 535 b upstream or downstream of the node failure 575.

In this example embodiment, a secondary backup LSP 574 a (logical), 574b (physical) may be employed to allow communications transporting media565 to flow to node D, which includes flowing the media 565 across theinitially disabled communications link 515 between the selected pair ofadjacent nodes 530 a, 530 b. A backup VPLS connection 573 a (logical),573 b (physical) rides on the secondary backup LSP 574 a, 574 b,respectively. The secondary backup LSP 574 a (logical) may be referredto as a “skip one” secondary backup LSP 574 a (logical) because it“skips” (logically) over the node failure 575 in the downstreamdirection. If two nodes downstream of a head-end ingress node, node A,fail, the example embodiment may use a “skip two” secondary backup LSP(not shown) in the downstream direction. Because communications cannotactually pass through the failed node 575, the “skip one” secondarybackup LSP 574 b (physical) traverses the physical links 515 of the ringnetwork 505, via the nodes 510 from node F to node D, including acrossthe re-enabled communications link 515 between the selected pair ofadjacent nodes 530 a, 530 b.

As illustrated in FIGS. 5A and 5B, distribution of media 565 can beinitially disabled on a communications link 515 to form a “horseshoe”topology in a ring network 505. Primary communications paths 520 totraverse the communications links 515, other than between the selectedpair of adjacent nodes 530 a, 530 b, can be configured, and primaryconnections 525 to distribute the media 565 to each of the nodes 510 onthe communications paths 520, including to the selected pair of adjacentnodes 530 a, 530 b, can also be configured. First backup communicationspaths 572 and 571 that use the primary connections 525 between adjacentnodes 510, other than between the selected pair of adjacent nodes 530 a,530 b, can be configured. Second backup communications paths 574 a(logical), 574 b (physical) and secondary connections 573 a (logical),573 b (physical) between non-adjacent nodes (e.g., nodes F and D) canalso be configured. In an example embodiment, the first backupcommunications paths 572 and 571 may be activated in an event of a linkfailure 570, and the second backup communications paths 574 a (logical),574 b (physical), 573 a (logical), 573 b (physical) may be activated inan event of a node failure 575.

Any number of second backup communications paths 574 a, 574 b can beconfigured in a manner as described above in reference to FIGS. 5A and5B, or as otherwise understood in the art, to support communicationsfailures on communications links or nodes. A Virtual Private Local AreaNetwork (LAN) Service (VPLS) connection may be used, or another form ofmulti-protocol label switching (MPLS) technique, may be used inaccordance with example embodiments of the invention. Label SwitchedPaths (LSPs) may be configured as the communications paths 520, 574 b,or other form of paths carrying communications supporting media 565 maybe employed.

FIG. 6 is a flow diagram 600 illustrating aspects of an exampleembodiment of the invention. The flow diagram begins (605) andconfigures a “horseshoe” network topology from a point of view of atleast some media (610). The “horseshoe” network topology is configuredfrom a ring network by disabling a communications link between aselected pair of adjacent nodes. Primary communications paths andconnections are configured (615). First backup communications paths,which use the primary connections, are configured between adjacent nodes(620). The second backup communications paths and secondary connectionsare configured between non-adjacent nodes (625). The flow diagram 600ends (630), allowing typical network communications to occur withfailover conditions facilitated by the first and second backupcommunications paths.

FIG. 7 is a block diagram 700 illustrating an example embodiment of theinvention in which a monitoring unit 710 and activation unit 715 may beemployed during operation of a network. The monitoring unit 710 mayreceive a communications link failure input 705 a and a node failureinput 705 b. It should be understood that the inputs 705 a, 705 b may bereceived on separate ports at the monitoring unit 710 or in a singleport (not shown) in the monitoring unit 710.

The input 705 a, 705 b may be in the form of communications, errorsignals, or other typical network signals used for such a purpose.Moreover, the communications link failure input 705 a or node failureinput 705 b may also be in the form of an absence of signals to themonitoring unit 710. Regardless, the monitoring unit 710, in an event ofa failure, may send failure information 715 to the activation unit 720.In turn, the activation unit 720 may process the failure information 715and determine whether to send activation data 725 a or 725 b to activatebackup communications paths that use primary connections betweenadjacent nodes 730 a or activate backup communications paths that usesecondary connections between adjacent nodes (e.g., every second node,third node, and so forth) (730 b).

It should be understood that the activation unit 720 may activate thebackup communications paths independently, via signaling through a MPLSsignaling protocol, provisioning channel, or other technique to activatethe backup communications path(s). Moreover, the activation unit 720 mayalso be employed to re-enable the disabled link between the selectedpair of adjacent nodes (e.g., nodes C and D 530 b, 530 a, respectively,in FIG. 5B) in accordance with the example embodiments described inreference to FIGS. 5A and 5B, or other figures described herein.

The monitoring unit 710 and activation unit 720 may be implemented inhardware, firmware, or software and may be employed in each node of aring network, at a central data collection node of a ring network, orother node associated with a ring network. If implemented in software,the monitoring unit 710 and/or activation unit 720 may be stored on anyform of computer-readable media in the form of processor instructions.The processor instructions can be loaded and executed by any form ofcustom or general processor adapted to operate in networkconfiguration(s) as described herein. In one example embodiment, themonitoring unit 710 and activation unit 720 may be available in softwarethat can be downloaded to some or all of the nodes of a ring network.

FIG. 8 is an example table 800 stored in one or more nodes in a ringnetwork, or associated with a ring network, that may be used to signal,provision, or provide instructions for manually configuring backupcommunications paths in an event of a communications link failure or anode failure in a link network.

First backup communications paths, which use primary connections betweenadjacent nodes, are indicated in the top row 805 of the table 800. Asillustrated, node A has a first backup communications path to node B,node B has a first backup communications path to node C, node C has afirst backup communications path to node D, . . . , and node n has afirst backup communications path to node A, which completes the firstbackup communications path around the ring network. It should beunderstood that backup communications paths may also be found traversingthe communications links of the ring network in the opposite direction(not shown for brevity).

The table 800 may also include an illustration of second backupcommunications paths, which use secondary connections betweennon-adjacent nodes, in the second row 810, third row, 815, fourth row820, and so forth. As illustrated, one of the second backupcommunications paths (row 810) has a “skip one” methodology, the nextlower row (row 815) of second backup communications paths has a “skiptwo” methodology, the next lower row (row 820) of second backupcommunications paths has a “skip three” methodology, and so forth.

The second backup communications paths can be preconfigured hierarchiesof paths or hierarchies of paths that are determined during operation.The multiple levels of hierarchy (i.e., rows 805, 810, 815, and 820, andso forth) may be employed as needed in an increasing order as failuresin a network occur. For example, if a communications link failureoccurs, the first backup communications paths (row 805) may beactivated. If a network node failure occurs, a “skip one” second backupcommunications path (row 810) may be activated. If two adjacent nodesfail, a “skip two” second backup communications path (row 815)methodology may be activated, and so forth.

While this invention has been particularly shown and described withreferences to example embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A method of managing faults in a ring network, comprising: disablingdistribution of media via a first communications link between a selectedpair of adjacent nodes among multiple nodes coupled by communicationslinks to form a ring network; disabling distribution of media via asecond communications link between a pair of adjacent ingress nodesamong the multiple nodes, each of the adjacent ingress nodes beingconfigured to receive the media via communications links external fromthe ring network; configuring (i) primary communications paths totraverse the communications links other than the first and secondcommunications links and (ii) primary connections to distribute themedia to each of the nodes on the primary communications paths,including the selected pair of adjacent nodes; configuring first backupcommunications paths that use the primary connections between adjacentnodes, other than between the selected pair of adjacent nodes andbetween the pair of adjacent ingress nodes; and configuring secondbackup communications paths and secondary connections betweennon-adjacent nodes.
 2. The method according to claim 1 wherein disablingdistribution of the media via the first communications link between theselected pair of adjacent nodes is dynamic and includes enablingdistribution of the media via the first communications link between theselected pair of adjacent nodes in an event a failure occurs on adifferent communications link.
 3. The method according to claim 1further comprising: monitoring the ring network for failures; andactivating the first or second backup communications paths andrespective connections in an event of detecting a failure.
 4. The methodaccording to claim 3 wherein activating the first or second backupcommunications paths in an event of detecting a failure includes:activating a corresponding first backup communications path in an eventof a communications link failure on the ring network; and activating acorresponding second backup communications path in an event of a nodefailure on the ring network.
 5. The method according to claim 1 whereinconfiguring the second backup communications paths and secondaryconnections includes selecting the non-adjacent nodes from at least oneof the following: every second node, every third node, and so forth onthe ring network.
 6. The method according to claim 1 wherein the primaryconnections and secondary connections are Virtual Private LAN Service(VPLS) connections.
 7. The method according to claim 1 wherein thecommunications paths are Label Switched Paths (LSPs).
 8. The methodaccording to claim 1 wherein the first or second backup communicationspaths span the ring, including between the selected pair of adjacentnodes.
 9. The method according to claim 1 further comprising creating ahierarchy of the second backup communications paths and secondaryconnections and advancing through the hierarchy based on failures andnumbers of failures in the ring network.
 10. The method according toclaim 9 further including backing-up through the hierarchy as thefailures are repaired.
 11. The method according to claim 1 wherein theingress nodes are configured to receive the media from a head-end nodevia the communications links external from the ring network.
 12. Anetwork comprising: multiple nodes interconnected by communicationslinks to form a ring network; a selected pair of adjacent nodes disabledfrom distributing media via a first communications link spanning betweenthe selected pair of adjacent nodes; a pair of adjacent ingress nodesdisabled from distributing media via a second communications linkspanning between the ingress nodes, each of the ingress nodes beingconfigured to receive the media via communications links external fromthe ring network; primary communications paths traversing thecommunications paths other than the first and second communicationslinks and primary connections configured to distribute the media to eachof the nodes on the communications paths, including to the selected pairof adjacent nodes; first backup communications paths that use theprimary connections between adjacent nodes other than between theselected pair of adjacent nodes and between the pair of adjacent ingressnodes; and second backup communications paths and secondary connectionsconfigured between non-adjacent nodes.
 13. The network according toclaim 12 wherein the selected pair of adjacent nodes is selected in adynamic manner and wherein, in an event a failure occurs on acommunications link other than between the selected pair of adjacentnodes, a communications link between the pair of adjacent nodes on eachside of the failed communications link is selected to be disabled. 14.The network according to claim 12 further including: at least onemonitoring unit that monitors the ring network for failures; and anactivation unit that activates the first or second backup communicationspaths and respective connections in an event of detecting a failure inthe ring network.
 15. The network according to claim 14 wherein theactivation unit activates a corresponding first backup communicationspath in an event of a communications link failure and a second backupcommunications path in an event of a node failure.
 16. The networkaccording to claim 12 wherein the second backup communications paths andsecondary connections are configured between non-adjacent nodes selectedfrom at least one of the following: every second node, every third node,and so forth on the ring network.
 17. The network according to claim 12wherein the primary connections and secondary connections are VirtualPrivate Local Area Network (LAN) Service (VPLS) connections.
 18. Thenetwork according to claim 12 wherein the communications paths are LabelSwitched Paths (LSPs).
 19. The network according to claim 12 wherein thefirst or second backup communications paths span the ring, includingbetween the selected pair of adjacent nodes.
 20. The network accordingto claim 12 further comprising a table storing a hierarchy of the secondbackup communications paths and secondary connections used to advancethrough the hierarchy based on failures and numbers of failures in thering network.
 21. The network according to claim 20 wherein the table isused to back-up through the hierarchy as the failures are repaired.